The present disclosure relates to subject matter contained in Japanese Patent applications No. 3-191339 (filed on Apr. 26, 1991) and No. 3-206618 (filed on May 14, 1991), which are expressly incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to a distal end part of an endoscope.
It is desirable that the distal end part of an endoscope should be as thin as possible because the thinner the distal end part, the more effectively it can be inserted into a hollow organ of the patient's body, so that the pain inflicted on the patient is minimized. In the case of an endoscope for inspection of the inside of a bronchial tube, for example, it is particularly necessary to minimize the outer diameter of the distal end part because it must be inserted into the inner part of the bronchial tube.
2. Description of the Prior Art
In the distal end part of an endoscope, a light guide fiber bundle for illuminating the observation field of view is disposed in parallel to an objective optical system. An illuminating lens for enlarging the illuminating range is disposed at the exit end of the light guide fiber bundle. In addition, a solid-state imaging device is disposed at a position where an observed image is formed by the objective optical system. These elements are incorporated in a distal end block.
However, the light guide fiber bundle is disposed rather close to the periphery of the distal end block because it extends side by side with the solid-state imaging device, which is thicker than the objective optical system. In the meantime, the diameter of the illuminating lens must be larger than that of the light guide fiber bundle.
Accordingly, the outer edge of the illuminating lens is close to the outer edge portion of the forward end of the distal end block, so that the wall of this portion of the distal end block is exceedingly thin. Therefore, it is likely that the illuminating lens will be readily broken on impact. In addition, since the forward end outer edge portion of the distal end block cannot be rounded satisfactorily but remains edgy, it may cut a mucous membrane in a hollow organ of the patient's body.
In order to prevent such problems, the forward end portion of the distal end block must be thick to a certain extent, resulting in deterioration of the insertability of the endoscope. Thus the endoscope cannot be inserted into a hollow organ of the patient's body effectively and with minimal pains to the patient.
In the meantime, the rear end portion of the distal end block is a thinner than the other portion because it is connected to an insert tube of the endoscope.
Accordingly, if the distal end block is formed as thin as possible, the rear end portion thereof, which is thinner than the other portion, is cut at the outer periphery thereof by a bore for passing built-in parts (i.e., optical fiber bundles, tubes, codes, etc.).
To cope with this problem, it has been conventional practice to cover such a cut portion with the distal end portion of a skin tube used to cover the insert tube.
In actual practice, however, if a skin tube 91 is attached in such a manner that the distal end portion thereof just covers a cut portion 92 of a distal end block 90, as shown in FIG. 7, the mere separation of a narrow bond area 93, between the end face of the skin tube 91 and the distal end block 90, causes water or other liquid to leak in the inside of the endoscope, resulting in a failure to use it.
If the distal end portion of the skin tube 91 is extended as far as the outer peripheral surface of the end portion of the distal end block 90 and bonded to the surface thereof, as shown in FIG. 8, it is possible to cover the cut portion 92 without the likelihood of leakage of water. In FIGS. 7 and 8, reference numeral 95 denotes the foremost one of the joint rings, constituting a bendable portion that is formed at the distal end of the insert tube.
However, if the distal end portion of the skin tube 91 is extended forwardly and bonded to the outer peripheral surface of the distal end block 90, the outer diameter of this portion of the distal end block 90 increases exceedingly, resulting in deterioration of the insertability of the endoscope into a hollow organ of the patient's body.